(1) Field of the Invention
The present invention relates to the field of communication technology. More specifically, the present invention relates to the field of encoding and decoding of communication information.
(2) Prior Art
In many systems there are often a group of information receiver stations that are coupled to receive messages from a central transmitter or station. This arrangement can exist in conjunction with a number of different communication technologies, such as cable video, cable TV, computer/network communication, telephone, wireless beepers, pagers and others. As with most utilities, typically the information transmitter offers several different receiver subscription levels that limit information reception for some receivers or, alternatively, the transmitter may desire to transmit special messages to only a select group of authorized receivers. However, in order to reduce the complexity of distributing information to the receivers, all receivers within a given network are typically coupled to, or receive information from, a common distribution cable or network communication bus. Therefore, some encoding procedure is required to discriminate among a select group of arbitrary receivers.
There arises the need for the capability to transmit certain messages such that only a subset (e.g., G) of the receivers of any particular network are able to receive certain messages and the other receivers do not. This is accomplished by transmitting messages in coded form using an encryption code that is known by the transmitter and only those authorized receivers that should validly receive the message. A uniform encryption key can be given between the transmitter (or source station) and the authorized receivers. This is a single standard key system. However, unauthorized receivers may pick up the standard key and then may be able to receive the message. Therefore, if a uniform or standard encryption key is used, it can be readily broken by unauthorized receivers. Although a valid mechanism in which to encrypt messages, the uniform or standard encryption key system is not desirable.
Other prior art methods of solving this problem utilize a separate or private encryption key for each authorized receiver within the network. Using this technique, the transmitter is aware of each private key and the standard or uniform key is broadcast in an encoded form, separately, to each authorized receiver. The authorized receiver then decodes the standard key, using its private key, and obtains the standard key or code by which it can decode the message. Although this method reduces the chances that an unauthorized receiver will receive the message (because the standard key is encoded), it unfortunately requires a transmission of a separate encoded standard key for each authorized receiver before the transmission of the message. This type of system is not practical in systems having large numbers of users, such as a cable video or TV system having hundreds of thousands of receivers, because the bandwidth required to communicate each encoded standard key to each receiver is too large. Further, in these systems, for security reasons, it is often desirable to alter or modify the private key for each receiver. Using the above system requires high bandwidth transmission in order to alter the private keys and a separate transmission is required for each authorized receiver.
FIG. 1 illustrates a typical procedure 50 utilized by these prior art systems that utilize the private key system as discussed above. The procedure 50 begins at 52 and flows to 54 where the transmitter generates and transmits a private encryption key, k(i), to each unit within the system. This step may be performed when the receivers are assembled before they are inserted into the communication network. In any case, at 54, a private key is given to each receiver and each private key is recorded in memory at the transmitter site. At 56, the transmitter generates a master encryption key, K, for all units and stores this standard key, K, into memory. The key, K, may be generated by a number of procedures, including random or arbitrary generation.
At 58, the transmitter encrypts key, K, a separate time using each private key, k(i), in order to generate a separate encrypted master key, K'(i), for each individual authorized receiver of the selected group of receivers (G). For instance: EQU K'(i)=E.sub.k(i) (K)
Where E.sub.k(i) (K) is the Encryption of K by individual private key k(i).
Also, at 58, each K'(i) is transmitted separately over the communication network (to all receivers) with the address of its associated receiver. This step requires a large bandwidth transmission because each authorized receiver must have a separate transmission performed. At 60, each receiver uses its private key, k(i), to decrypt its associated K'(i) in order to obtain the standard key, K, which it stores. Each authorized receiver (the set G) would obtain a valid K. Receivers outside of G would not receive a valid K. Since they would not receive an encoded K'(i) that they could decode. For instance: EQU K=D.sub.k(i) (K'(i))
Where D.sub.k(i) (K'(i)) is the Decryption of K'(i) by private key k(i)
At 62, the transmitter encrypts a message, M, using the standard key, K, and broadcasts the encrypted message, C, to all users. At 64, each authorized receiver (e.g., the set of G), having a valid K, will decrypt the message C to obtain the message M and will process the message M in conventional methods. Those receivers not in G would not have a valid K and therefore would not be able to obtain M. Although valid, the prior art process 50 is not desirable because of the large bandwidth requirements of block 58.
What is needed is system that offers the protection and security level of a system having private keys for each receiver, but offers the low bandwidth requirements of a single standard key system. The present invention offers such advantageous functionality.
Accordingly, it is an object of the present invention to provide efficient broadcast and reception of messages to a selected subset, G, of receivers of a larger group of receivers within a communication network. It is an object of the present invention to provide such efficient broadcast using low bandwidth requirements but also allowing use of private keys for each receiver. Therefore, it is an object of the present invention to provide the security level offered by private key systems while maintaining the low bandwidth requirements of a single standard key system. It is also an object of the present invention to provide a low bandwidth requirement mechanism for broadcasting replacement private keys to all receivers within a network or a select subset of receivers. These and other objects not specifically mentioned, but that are clear within discussions of the present invention, will be discussed to follow.